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 $87.73   8.435%   $95.13   $95.13   $95.15   $95.10  
  Purchase #2 $238.27   11.435%   $265.5162   $265.52   $265.50   $265.50  
  Purchase #3 $173.67   10.534%   $191.9644   $191.96   $191.95   $192.00  
  Purchase #4 $95.43   9.740%   $104.7249   $104.72   $104.70   $104.70  
  Purchase #5 $130.25   8.245%   $140.9891   $140.99   $141.00   $141.00  
  Purchase #6 $116.85   8.150%   $126.3733   $126.37   $126.35   $126.40  
  Purchase #7 $66.72   3.845%   $69.2854   $69.29   $69.30   $69.30  
  7 purchase totals = $908.92       $993.9833   $993.98   $993.95   $994.00