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 $69.29   11.405%   $77.1925   $77.19   $77.20   $77.20  
  Purchase #2 $193.56   8.686%   $210.3726   $210.37   $210.35   $210.40  
  Purchase #3 $75.35   8.751%   $81.9439   $81.94   $81.95   $81.90  
  Purchase #4 $188.65   13.502%   $214.1215   $214.12   $214.10   $214.10  
  Purchase #5 $125.44   11.527%   $139.8995   $139.90   $139.90   $139.90  
  Purchase #6 $195.33   4.270%   $203.6706   $203.67   $203.65   $203.70  
  Purchase #7 $47.98   12.714%   $54.0802   $54.08   $54.10   $54.10  
  7 purchase totals = $895.60       $981.2808   $981.27   $981.25   $981.30