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 $88.25   4.471%   $92.1957   $92.20   $92.20   $92.20  
  Purchase #2 $227.58   11.419%   $253.5674   $253.57   $253.55   $253.60  
  Purchase #3 $103.48   4.308%   $107.9379   $107.94   $107.95   $107.90  
  Purchase #4 $146.48   13.167%   $165.767   $165.77   $165.75   $165.80  
  Purchase #5 $152.98   9.239%   $167.1138   $167.11   $167.10   $167.10  
  Purchase #6 $208.27   10.398%   $229.9259   $229.93   $229.95   $229.90  
  Purchase #7 $58.36   8.415%   $63.271   $63.27   $63.25   $63.30  
  7 purchase totals = $985.40       $1,079.7787   $1,079.79   $1,079.75   $1,079.80