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 $86.66   8.842%   $94.3225   $94.32   $94.30   $94.30  
  Purchase #2 $203.67   11.121%   $226.3201   $226.32   $226.30   $226.30  
  Purchase #3 $243.82   9.656%   $267.3633   $267.36   $267.35   $267.40  
  Purchase #4 $159.29   5.573%   $168.1672   $168.17   $168.15   $168.20  
  Purchase #5 $151.65   9.225%   $165.6397   $165.64   $165.65   $165.60  
  Purchase #6 $53.74   7.601%   $57.8248   $57.82   $57.80   $57.80  
  Purchase #7 $152.61   11.587%   $170.2929   $170.29   $170.30   $170.30  
  7 purchase totals = $1,051.44       $1,149.9305   $1,149.92   $1,149.85   $1,149.90