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 $184.91   9.801%   $203.033   $203.03   $203.05   $203.00  
  Purchase #2 $130.90   12.837%   $147.7036   $147.70   $147.70   $147.70  
  Purchase #3 $132.56   13.445%   $150.3827   $150.38   $150.40   $150.40  
  Purchase #4 $102.75   13.636%   $116.761   $116.76   $116.75   $116.80  
  Purchase #5 $131.27   5.360%   $138.3061   $138.31   $138.30   $138.30  
  Purchase #6 $245.30   12.452%   $275.8448   $275.84   $275.85   $275.80  
  Purchase #7 $63.76   9.628%   $69.8988   $69.90   $69.90   $69.90  
  7 purchase totals = $991.45       $1,101.9300   $1,101.92   $1,101.95   $1,101.90