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 $71.49   6.813%   $76.3606   $76.36   $76.35   $76.40  
  Purchase #2 $116.96   11.744%   $130.6958   $130.70   $130.70   $130.70  
  Purchase #3 $16.79   5.550%   $17.7218   $17.72   $17.70   $17.70  
  Purchase #4 $169.94   4.431%   $177.47   $177.47   $177.45   $177.50  
  Purchase #5 $240.77   11.424%   $268.2756   $268.28   $268.30   $268.30  
  Purchase #6 $143.85   4.472%   $150.283   $150.28   $150.30   $150.30  
  Purchase #7 $198.29   5.435%   $209.0671   $209.07   $209.05   $209.10  
  7 purchase totals = $958.09       $1,029.8739   $1,029.88   $1,029.85   $1,030.00