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 $232.84   13.527%   $264.3363   $264.34   $264.35   $264.30  
  Purchase #2 $223.65   9.215%   $244.2593   $244.26   $244.25   $244.30  
  Purchase #3 $65.46   3.841%   $67.9743   $67.97   $67.95   $68.00  
  Purchase #4 $196.30   7.214%   $210.4611   $210.46   $210.45   $210.50  
  Purchase #5 $249.75   13.397%   $283.209   $283.21   $283.20   $283.20  
  Purchase #6 $221.96   11.596%   $247.6985   $247.70   $247.70   $247.70  
  Purchase #7 $205.68   10.367%   $227.0028   $227.00   $227.00   $227.00  
  7 purchase totals = $1,395.64       $1,544.9413   $1,544.94   $1,544.90   $1,545.00