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 $204.35   9.701%   $224.174   $224.17   $224.15   $224.20  
  Purchase #2 $72.97   4.218%   $76.0479   $76.05   $76.05   $76.00  
  Purchase #3 $223.90   3.813%   $232.4373   $232.44   $232.45   $232.40  
  Purchase #4 $244.89   13.637%   $278.2856   $278.29   $278.30   $278.30  
  Purchase #5 $59.74   11.222%   $66.444   $66.44   $66.45   $66.40  
  Purchase #6 $226.57   13.805%   $257.848   $257.85   $257.85   $257.80  
  Purchase #7 $81.94   8.118%   $88.5919   $88.59   $88.60   $88.60  
  7 purchase totals = $1,114.36       $1,223.8287   $1,223.83   $1,223.85   $1,223.70