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 $204.34   11.216%   $227.2588   $227.26   $227.25   $227.30  
  Purchase #2 $197.49   7.646%   $212.5901   $212.59   $212.60   $212.60  
  Purchase #3 $7.78   5.165%   $8.1818   $8.18   $8.20   $8.20  
  Purchase #4 $134.85   12.359%   $151.5161   $151.52   $151.50   $151.50  
  Purchase #5 $239.49   6.188%   $254.3096   $254.31   $254.30   $254.30  
  Purchase #6 $193.54   5.400%   $203.9912   $203.99   $204.00   $204.00  
  Purchase #7 $196.83   5.496%   $207.6478   $207.65   $207.65   $207.60  
  7 purchase totals = $1,174.32       $1,265.4954   $1,265.50   $1,265.50   $1,265.50