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 $87.94   6.851%   $93.9648   $93.96   $93.95   $94.00  
  Purchase #2 $105.85   4.172%   $110.2661   $110.27   $110.25   $110.30  
  Purchase #3 $247.52   3.363%   $255.8441   $255.84   $255.85   $255.80  
  Purchase #4 $197.45   9.714%   $216.6303   $216.63   $216.65   $216.60  
  Purchase #5 $222.32   8.462%   $241.1327   $241.13   $241.15   $241.10  
  Purchase #6 $29.55   10.704%   $32.713   $32.71   $32.70   $32.70  
  Purchase #7 $96.46   11.158%   $107.223   $107.22   $107.20   $107.20  
  7 purchase totals = $987.09       $1,057.7740   $1,057.76   $1,057.75   $1,057.70