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 $191.93   6.272%   $203.9678   $203.97   $203.95   $204.00  
  Purchase #2 $217.58   4.870%   $228.1761   $228.18   $228.20   $228.20  
  Purchase #3 $11.91   13.175%   $13.4791   $13.48   $13.50   $13.50  
  Purchase #4 $36.51   12.813%   $41.188   $41.19   $41.20   $41.20  
  Purchase #5 $65.62   4.808%   $68.775   $68.78   $68.80   $68.80  
  Purchase #6 $181.92   13.529%   $206.532   $206.53   $206.55   $206.50  
  Purchase #7 $230.34   6.642%   $245.6392   $245.64   $245.65   $245.60  
  7 purchase totals = $935.81       $1,007.7572   $1,007.77   $1,007.85   $1,007.80