Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $147.44   12.166%   $165.3776   $165.38   $165.40   $165.40  
  Purchase #2 $243.75   12.226%   $273.5509   $273.55   $273.55   $273.60  
  Purchase #3 $216.69   3.654%   $224.6079   $224.61   $224.60   $224.60  
  Purchase #4 $99.48   7.338%   $106.7798   $106.78   $106.80   $106.80  
  Purchase #5 $140.94   5.817%   $149.1385   $149.14   $149.15   $149.10  
  Purchase #6 $238.25   6.126%   $252.8452   $252.85   $252.85   $252.80  
  Purchase #7 $118.64   6.255%   $126.0609   $126.06   $126.05   $126.10  
  7 purchase totals = $1,205.19       $1,298.3608   $1,298.37   $1,298.40   $1,298.40