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 $224.27   12.829%   $253.0416   $253.04   $253.05   $253.00  
  Purchase #2 $101.81   6.137%   $108.0581   $108.06   $108.05   $108.10  
  Purchase #3 $232.26   4.780%   $243.362   $243.36   $243.35   $243.40  
  Purchase #4 $63.50   9.486%   $69.5236   $69.52   $69.50   $69.50  
  Purchase #5 $189.81   5.150%   $199.5852   $199.59   $199.60   $199.60  
  Purchase #6 $8.35   6.324%   $8.8781   $8.88   $8.90   $8.90  
  Purchase #7 $41.41   7.817%   $44.647   $44.65   $44.65   $44.60  
  7 purchase totals = $861.41       $927.0956   $927.10   $927.10   $927.10