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 $214.94   9.607%   $235.5893   $235.59   $235.60   $235.60  
  Purchase #2 $165.97   12.873%   $187.3353   $187.34   $187.35   $187.30  
  Purchase #3 $177.48   13.405%   $201.2712   $201.27   $201.25   $201.30  
  Purchase #4 $84.95   7.378%   $91.2176   $91.22   $91.20   $91.20  
  Purchase #5 $7.29   10.223%   $8.0353   $8.04   $8.05   $8.00  
  Purchase #6 $54.92   10.356%   $60.6075   $60.61   $60.60   $60.60  
  Purchase #7 $20.88   9.612%   $22.887   $22.89   $22.90   $22.90  
  7 purchase totals = $726.43       $806.9432   $806.96   $806.95   $806.90