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 $55.75   3.296%   $57.5875   $57.59   $57.60   $57.60  
  Purchase #2 $238.91   11.104%   $265.4386   $265.44   $265.45   $265.40  
  Purchase #3 $7.56   12.478%   $8.5033   $8.50   $8.50   $8.50  
  Purchase #4 $190.84   6.143%   $202.5633   $202.56   $202.55   $202.60  
  Purchase #5 $56.52   9.735%   $62.0222   $62.02   $62.00   $62.00  
  Purchase #6 $145.87   4.197%   $151.9922   $151.99   $152.00   $152.00  
  Purchase #7 $72.60   5.864%   $76.8573   $76.86   $76.85   $76.90  
  7 purchase totals = $768.05       $824.9644   $824.96   $824.95   $825.00