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 $80.66   5.822%   $85.356   $85.36   $85.35   $85.40  
  Purchase #2 $23.95   12.337%   $26.9047   $26.90   $26.90   $26.90  
  Purchase #3 $57.84   13.865%   $65.8595   $65.86   $65.85   $65.90  
  Purchase #4 $79.58   9.673%   $87.2778   $87.28   $87.30   $87.30  
  Purchase #5 $188.92   8.573%   $205.1161   $205.12   $205.10   $205.10  
  Purchase #6 $245.50   10.461%   $271.1818   $271.18   $271.20   $271.20  
  Purchase #7 $223.60   12.271%   $251.038   $251.04   $251.05   $251.00  
  7 purchase totals = $900.05       $992.7339   $992.74   $992.75   $992.80