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 $152.33   9.523%   $166.8364   $166.84   $166.85   $166.80  
  Purchase #2 $67.44   8.571%   $73.2203   $73.22   $73.20   $73.20  
  Purchase #3 $209.78   11.618%   $234.1522   $234.15   $234.15   $234.20  
  Purchase #4 $105.94   7.387%   $113.7658   $113.77   $113.75   $113.80  
  Purchase #5 $96.94   13.188%   $109.7244   $109.72   $109.70   $109.70  
  Purchase #6 $219.43   12.424%   $246.692   $246.69   $246.70   $246.70  
  Purchase #7 $140.42   9.245%   $153.4018   $153.40   $153.40   $153.40  
  7 purchase totals = $992.28       $1,097.7929   $1,097.79   $1,097.75   $1,097.80