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 $88.66   13.493%   $100.6229   $100.62   $100.60   $100.60  
  Purchase #2 $165.98   4.391%   $173.2682   $173.27   $173.25   $173.30  
  Purchase #3 $193.82   4.707%   $202.9431   $202.94   $202.95   $202.90  
  Purchase #4 $173.54   5.476%   $183.0431   $183.04   $183.05   $183.00  
  Purchase #5 $25.96   13.346%   $29.4246   $29.42   $29.40   $29.40  
  Purchase #6 $199.55   11.340%   $222.179   $222.18   $222.20   $222.20  
  Purchase #7 $229.65   6.768%   $245.1927   $245.19   $245.20   $245.20  
  7 purchase totals = $1,077.16       $1,156.6736   $1,156.66   $1,156.65   $1,156.60