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 $217.84   11.835%   $243.6214   $243.62   $243.60   $243.60  
  Purchase #2 $102.39   7.785%   $110.3611   $110.36   $110.35   $110.40  
  Purchase #3 $169.43   6.861%   $181.0546   $181.05   $181.05   $181.10  
  Purchase #4 $139.92   6.862%   $149.5213   $149.52   $149.50   $149.50  
  Purchase #5 $184.30   13.682%   $209.5159   $209.52   $209.50   $209.50  
  Purchase #6 $226.60   11.243%   $252.0766   $252.08   $252.10   $252.10  
  Purchase #7 $93.95   5.223%   $98.857   $98.86   $98.85   $98.90  
  7 purchase totals = $1,134.43       $1,245.0079   $1,245.01   $1,244.95   $1,245.10