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 $83.61   11.159%   $92.94   $92.94   $92.95   $92.90  
  Purchase #2 $142.48   7.755%   $153.5293   $153.53   $153.55   $153.50  
  Purchase #3 $151.65   9.376%   $165.8687   $165.87   $165.85   $165.90  
  Purchase #4 $178.55   12.817%   $201.4348   $201.43   $201.45   $201.40  
  Purchase #5 $96.75   4.791%   $101.3853   $101.39   $101.40   $101.40  
  Purchase #6 $193.35   4.736%   $202.5071   $202.51   $202.50   $202.50  
  Purchase #7 $145.73   3.464%   $150.7781   $150.78   $150.80   $150.80  
  7 purchase totals = $992.12       $1,068.4433   $1,068.45   $1,068.50   $1,068.40