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 $216.53   8.180%   $234.2422   $234.24   $234.25   $234.20  
  Purchase #2 $99.95   9.170%   $109.1154   $109.12   $109.10   $109.10  
  Purchase #3 $232.53   6.509%   $247.6654   $247.67   $247.65   $247.70  
  Purchase #4 $9.65   13.385%   $10.9417   $10.94   $10.95   $10.90  
  Purchase #5 $165.78   9.594%   $181.6849   $181.68   $181.70   $181.70  
  Purchase #6 $138.57   8.290%   $150.0575   $150.06   $150.05   $150.10  
  Purchase #7 $31.48   7.775%   $33.9276   $33.93   $33.95   $33.90  
  7 purchase totals = $894.49       $967.6347   $967.64   $967.65   $967.60