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 $178.69   12.308%   $200.6832   $200.68   $200.70   $200.70  
  Purchase #2 $102.96   11.279%   $114.5729   $114.57   $114.55   $114.60  
  Purchase #3 $5.42   5.173%   $5.7004   $5.70   $5.70   $5.70  
  Purchase #4 $186.95   5.363%   $196.9761   $196.98   $197.00   $197.00  
  Purchase #5 $44.68   13.803%   $50.8472   $50.85   $50.85   $50.80  
  Purchase #6 $167.66   4.828%   $175.7546   $175.75   $175.75   $175.80  
  Purchase #7 $150.56   13.200%   $170.4339   $170.43   $170.45   $170.40  
  7 purchase totals = $836.92       $914.9683   $914.96   $915.00   $915.00