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 $192.42   10.620%   $212.855   $212.86   $212.85   $212.90  
  Purchase #2 $91.35   13.541%   $103.7197   $103.72   $103.70   $103.70  
  Purchase #3 $239.42   8.700%   $260.2495   $260.25   $260.25   $260.20  
  Purchase #4 $84.30   4.533%   $88.1213   $88.12   $88.10   $88.10  
  Purchase #5 $244.30   4.319%   $254.8513   $254.85   $254.85   $254.90  
  Purchase #6 $50.98   9.335%   $55.739   $55.74   $55.75   $55.70  
  Purchase #7 $108.25   13.609%   $122.9817   $122.98   $123.00   $123.00  
  7 purchase totals = $1,011.02       $1,098.5175   $1,098.52   $1,098.50   $1,098.50