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 $24.97   4.717%   $26.1478   $26.15   $26.15   $26.10  
  Purchase #2 $176.52   13.221%   $199.8577   $199.86   $199.85   $199.90  
  Purchase #3 $182.85   3.420%   $189.1035   $189.10   $189.10   $189.10  
  Purchase #4 $214.59   3.212%   $221.4826   $221.48   $221.50   $221.50  
  Purchase #5 $246.50   9.731%   $270.4869   $270.49   $270.50   $270.50  
  Purchase #6 $105.94   4.761%   $110.9838   $110.98   $111.00   $111.00  
  Purchase #7 $149.89   11.297%   $166.8231   $166.82   $166.80   $166.80  
  7 purchase totals = $1,101.26       $1,184.8854   $1,184.88   $1,184.90   $1,184.90