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 $226.90   8.703%   $246.6471   $246.65   $246.65   $246.60  
  Purchase #2 $184.62   4.692%   $193.2824   $193.28   $193.30   $193.30  
  Purchase #3 $25.74   13.802%   $29.2926   $29.29   $29.30   $29.30  
  Purchase #4 $209.70   10.660%   $232.054   $232.05   $232.05   $232.10  
  Purchase #5 $118.92   7.669%   $128.04   $128.04   $128.05   $128.00  
  Purchase #6 $160.50   4.213%   $167.2619   $167.26   $167.25   $167.30  
  Purchase #7 $132.71   4.497%   $138.678   $138.68   $138.70   $138.70  
  7 purchase totals = $1,059.09       $1,135.2560   $1,135.25   $1,135.30   $1,135.30