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 $246.78   11.205%   $274.4317   $274.43   $274.45   $274.40  
  Purchase #2 $124.79   10.214%   $137.5361   $137.54   $137.55   $137.50  
  Purchase #3 $79.27   11.319%   $88.2426   $88.24   $88.25   $88.20  
  Purchase #4 $48.41   8.843%   $52.6909   $52.69   $52.70   $52.70  
  Purchase #5 $212.93   9.214%   $232.5494   $232.55   $232.55   $232.50  
  Purchase #6 $61.95   4.183%   $64.5414   $64.54   $64.55   $64.50  
  Purchase #7 $165.32   9.233%   $180.584   $180.58   $180.60   $180.60  
  7 purchase totals = $939.45       $1,030.5761   $1,030.57   $1,030.65   $1,030.40