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 $175.72   7.872%   $189.5527   $189.55   $189.55   $189.60  
  Purchase #2 $60.55   8.435%   $65.6574   $65.66   $65.65   $65.70  
  Purchase #3 $243.40   13.817%   $277.0306   $277.03   $277.05   $277.00  
  Purchase #4 $85.44   8.541%   $92.7374   $92.74   $92.75   $92.70  
  Purchase #5 $152.37   8.841%   $165.841   $165.84   $165.85   $165.80  
  Purchase #6 $184.83   9.802%   $202.947   $202.95   $202.95   $202.90  
  Purchase #7 $58.45   4.797%   $61.2538   $61.25   $61.25   $61.30  
  7 purchase totals = $960.76       $1,055.0199   $1,055.02   $1,055.05   $1,055.00