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 $62.56   6.120%   $66.3887   $66.39   $66.40   $66.40  
  Purchase #2 $244.70   5.373%   $257.8477   $257.85   $257.85   $257.80  
  Purchase #3 $169.85   3.276%   $175.4143   $175.41   $175.40   $175.40  
  Purchase #4 $104.60   8.137%   $113.1113   $113.11   $113.10   $113.10  
  Purchase #5 $167.73   5.365%   $176.7287   $176.73   $176.75   $176.70  
  Purchase #6 $184.33   9.260%   $201.399   $201.40   $201.40   $201.40  
  Purchase #7 $40.79   6.727%   $43.5339   $43.53   $43.55   $43.50  
  7 purchase totals = $974.56       $1,034.4236   $1,034.42   $1,034.45   $1,034.30