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 $201.41   12.369%   $226.3224   $226.32   $226.30   $226.30  
  Purchase #2 $63.94   3.168%   $65.9656   $65.97   $65.95   $66.00  
  Purchase #3 $121.68   3.666%   $126.1408   $126.14   $126.15   $126.10  
  Purchase #4 $234.86   5.238%   $247.162   $247.16   $247.15   $247.20  
  Purchase #5 $187.66   11.550%   $209.3347   $209.33   $209.35   $209.30  
  Purchase #6 $198.56   13.460%   $225.2862   $225.29   $225.30   $225.30  
  Purchase #7 $210.95   4.140%   $219.6833   $219.68   $219.70   $219.70  
  7 purchase totals = $1,219.06       $1,319.8950   $1,319.89   $1,319.90   $1,319.90