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 $141.37   4.424%   $147.6242   $147.62   $147.60   $147.60  
  Purchase #2 $218.37   10.320%   $240.9058   $240.91   $240.90   $240.90  
  Purchase #3 $158.32   12.647%   $178.3427   $178.34   $178.35   $178.30  
  Purchase #4 $150.80   9.767%   $165.5286   $165.53   $165.55   $165.50  
  Purchase #5 $83.51   4.290%   $87.0926   $87.09   $87.10   $87.10  
  Purchase #6 $99.55   8.142%   $107.6554   $107.66   $107.65   $107.70  
  Purchase #7 $118.76   6.500%   $126.4794   $126.48   $126.50   $126.50  
  7 purchase totals = $970.68       $1,053.6287   $1,053.63   $1,053.65   $1,053.60