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 $194.74   3.661%   $201.8694   $201.87   $201.85   $201.90  
  Purchase #2 $119.52   11.254%   $132.9708   $132.97   $132.95   $133.00  
  Purchase #3 $67.81   6.634%   $72.3085   $72.31   $72.30   $72.30  
  Purchase #4 $225.66   4.541%   $235.9072   $235.91   $235.90   $235.90  
  Purchase #5 $130.59   6.633%   $139.252   $139.25   $139.25   $139.30  
  Purchase #6 $118.69   8.241%   $128.4712   $128.47   $128.45   $128.50  
  Purchase #7 $239.94   6.241%   $254.9147   $254.91   $254.90   $254.90  
  7 purchase totals = $1,096.95       $1,165.6938   $1,165.69   $1,165.60   $1,165.80