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 $219.31   13.434%   $248.7721   $248.77   $248.75   $248.80  
  Purchase #2 $246.53   4.284%   $257.0913   $257.09   $257.10   $257.10  
  Purchase #3 $95.64   5.731%   $101.1211   $101.12   $101.10   $101.10  
  Purchase #4 $122.74   10.110%   $135.149   $135.15   $135.15   $135.10  
  Purchase #5 $210.33   10.794%   $233.033   $233.03   $233.05   $233.00  
  Purchase #6 $147.97   7.282%   $158.7452   $158.75   $158.75   $158.70  
  Purchase #7 $102.60   13.424%   $116.373   $116.37   $116.35   $116.40  
  7 purchase totals = $1,145.12       $1,250.2847   $1,250.28   $1,250.25   $1,250.20