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 $212.98   7.279%   $228.4828   $228.48   $228.50   $228.50  
  Purchase #2 $98.32   4.730%   $102.9705   $102.97   $102.95   $103.00  
  Purchase #3 $56.30   12.830%   $63.5233   $63.52   $63.50   $63.50  
  Purchase #4 $248.96   9.172%   $271.7946   $271.79   $271.80   $271.80  
  Purchase #5 $68.54   3.664%   $71.0513   $71.05   $71.05   $71.10  
  Purchase #6 $89.43   3.594%   $92.6441   $92.64   $92.65   $92.60  
  Purchase #7 $178.31   7.631%   $191.9168   $191.92   $191.90   $191.90  
  7 purchase totals = $952.84       $1,022.3834   $1,022.37   $1,022.35   $1,022.40