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 $66.31   3.581%   $68.6846   $68.68   $68.70   $68.70  
  Purchase #2 $6.27   13.462%   $7.1141   $7.11   $7.10   $7.10  
  Purchase #3 $78.71   12.625%   $88.6471   $88.65   $88.65   $88.60  
  Purchase #4 $202.68   10.257%   $223.4689   $223.47   $223.45   $223.50  
  Purchase #5 $181.27   10.379%   $200.084   $200.08   $200.10   $200.10  
  Purchase #6 $219.59   13.201%   $248.5781   $248.58   $248.60   $248.60  
  Purchase #7 $69.85   11.146%   $77.6355   $77.64   $77.65   $77.60  
  7 purchase totals = $824.68       $914.2123   $914.21   $914.25   $914.20