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 $181.92   12.400%   $204.4781   $204.48   $204.50   $204.50  
  Purchase #2 $221.29   10.317%   $244.1205   $244.12   $244.10   $244.10  
  Purchase #3 $155.26   9.458%   $169.9445   $169.94   $169.95   $169.90  
  Purchase #4 $249.82   10.297%   $275.544   $275.54   $275.55   $275.50  
  Purchase #5 $209.48   6.709%   $223.534   $223.53   $223.55   $223.50  
  Purchase #6 $6.48   10.315%   $7.1484   $7.15   $7.15   $7.10  
  Purchase #7 $202.74   6.555%   $216.0296   $216.03   $216.05   $216.00  
  7 purchase totals = $1,226.99       $1,340.7991   $1,340.79   $1,340.85   $1,340.60