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 $87.52   9.291%   $95.6515   $95.65   $95.65   $95.70  
  Purchase #2 $229.84   5.244%   $241.8928   $241.89   $241.90   $241.90  
  Purchase #3 $82.51   3.641%   $85.5142   $85.51   $85.50   $85.50  
  Purchase #4 $153.98   7.134%   $164.9649   $164.96   $164.95   $165.00  
  Purchase #5 $90.73   7.396%   $97.4404   $97.44   $97.45   $97.40  
  Purchase #6 $29.99   11.607%   $33.4709   $33.47   $33.45   $33.50  
  Purchase #7 $106.48   12.823%   $120.1339   $120.13   $120.15   $120.10  
  7 purchase totals = $781.05       $839.0686   $839.05   $839.05   $839.10