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 $214.25   12.615%   $241.2776   $241.28   $241.30   $241.30  
  Purchase #2 $172.88   12.517%   $194.5194   $194.52   $194.50   $194.50  
  Purchase #3 $213.77   9.445%   $233.9606   $233.96   $233.95   $234.00  
  Purchase #4 $45.79   8.769%   $49.8053   $49.81   $49.80   $49.80  
  Purchase #5 $202.41   8.753%   $220.1269   $220.13   $220.15   $220.10  
  Purchase #6 $53.94   13.582%   $61.2661   $61.27   $61.25   $61.30  
  Purchase #7 $225.93   9.605%   $247.6306   $247.63   $247.65   $247.60  
  7 purchase totals = $1,128.97       $1,248.5865   $1,248.60   $1,248.60   $1,248.60