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 $68.57   10.283%   $75.6211   $75.62   $75.60   $75.60  
  Purchase #2 $27.95   13.837%   $31.8174   $31.82   $31.80   $31.80  
  Purchase #3 $145.45   6.261%   $154.5566   $154.56   $154.55   $154.60  
  Purchase #4 $46.49   9.818%   $51.0544   $51.05   $51.05   $51.10  
  Purchase #5 $235.95   10.568%   $260.8852   $260.89   $260.90   $260.90  
  Purchase #6 $243.32   11.220%   $270.6205   $270.62   $270.60   $270.60  
  Purchase #7 $166.53   7.201%   $178.5218   $178.52   $178.50   $178.50  
  7 purchase totals = $934.26       $1,023.0770   $1,023.08   $1,023.00   $1,023.10