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 $76.46   8.663%   $83.0837   $83.08   $83.10   $83.10  
  Purchase #2 $112.84   10.730%   $124.9477   $124.95   $124.95   $124.90  
  Purchase #3 $148.87   13.601%   $169.1178   $169.12   $169.10   $169.10  
  Purchase #4 $33.40   6.532%   $35.5817   $35.58   $35.60   $35.60  
  Purchase #5 $204.73   12.676%   $230.6816   $230.68   $230.70   $230.70  
  Purchase #6 $187.31   9.484%   $205.0745   $205.07   $205.05   $205.10  
  Purchase #7 $223.65   9.668%   $245.2725   $245.27   $245.25   $245.30  
  7 purchase totals = $987.26       $1,093.7595   $1,093.75   $1,093.75   $1,093.80