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 $60.43   5.325%   $63.6479   $63.65   $63.65   $63.60  
  Purchase #2 $60.85   5.672%   $64.3014   $64.30   $64.30   $64.30  
  Purchase #3 $137.60   8.532%   $149.34   $149.34   $149.35   $149.30  
  Purchase #4 $36.82   13.123%   $41.6519   $41.65   $41.65   $41.70  
  Purchase #5 $72.87   6.722%   $77.7683   $77.77   $77.75   $77.80  
  Purchase #6 $156.29   6.168%   $165.93   $165.93   $165.95   $165.90  
  Purchase #7 $212.49   10.746%   $235.3242   $235.32   $235.30   $235.30  
  7 purchase totals = $737.35       $797.9637   $797.96   $797.95   $797.90