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 $219.66   3.437%   $227.2097   $227.21   $227.20   $227.20  
  Purchase #2 $43.98   4.515%   $45.9657   $45.97   $45.95   $46.00  
  Purchase #3 $37.37   11.435%   $41.6433   $41.64   $41.65   $41.60  
  Purchase #4 $86.58   6.718%   $92.3964   $92.40   $92.40   $92.40  
  Purchase #5 $31.74   5.299%   $33.4219   $33.42   $33.40   $33.40  
  Purchase #6 $72.33   6.564%   $77.0777   $77.08   $77.10   $77.10  
  Purchase #7 $230.25   3.607%   $238.5551   $238.56   $238.55   $238.60  
  7 purchase totals = $721.91       $756.2698   $756.28   $756.25   $756.30