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 $202.37   12.142%   $226.9418   $226.94   $226.95   $226.90  
  Purchase #2 $223.78   9.196%   $244.3588   $244.36   $244.35   $244.40  
  Purchase #3 $79.97   8.817%   $87.021   $87.02   $87.00   $87.00  
  Purchase #4 $152.35   3.687%   $157.9671   $157.97   $157.95   $158.00  
  Purchase #5 $167.91   5.115%   $176.4986   $176.50   $176.50   $176.50  
  Purchase #6 $54.80   12.362%   $61.5744   $61.57   $61.55   $61.60  
  Purchase #7 $219.77   11.792%   $245.6853   $245.69   $245.70   $245.70  
  7 purchase totals = $1,100.95       $1,200.0470   $1,200.05   $1,200.00   $1,200.10