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 $203.26   7.424%   $218.35   $218.35   $218.35   $218.40  
  Purchase #2 $10.56   13.180%   $11.9518   $11.95   $11.95   $12.00  
  Purchase #3 $23.26   4.444%   $24.2937   $24.29   $24.30   $24.30  
  Purchase #4 $187.73   3.715%   $194.7042   $194.70   $194.70   $194.70  
  Purchase #5 $101.58   9.825%   $111.5602   $111.56   $111.55   $111.60  
  Purchase #6 $178.29   7.585%   $191.8133   $191.81   $191.80   $191.80  
  Purchase #7 $115.90   6.399%   $123.3164   $123.32   $123.30   $123.30  
  7 purchase totals = $820.58       $875.9896   $875.98   $875.95   $876.10