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 $154.78   8.312%   $167.6453   $167.65   $167.65   $167.60  
  Purchase #2 $66.29   3.506%   $68.6141   $68.61   $68.60   $68.60  
  Purchase #3 $87.78   12.792%   $99.0088   $99.01   $99.00   $99.00  
  Purchase #4 $51.56   5.844%   $54.5732   $54.57   $54.55   $54.60  
  Purchase #5 $244.62   4.444%   $255.4909   $255.49   $255.50   $255.50  
  Purchase #6 $165.95   11.615%   $185.2251   $185.23   $185.25   $185.20  
  Purchase #7 $179.51   13.775%   $204.2375   $204.24   $204.25   $204.20  
  7 purchase totals = $950.49       $1,034.7949   $1,034.80   $1,034.80   $1,034.70