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 $87.77   11.219%   $97.6169   $97.62   $97.60   $97.60  
  Purchase #2 $62.37   13.276%   $70.6502   $70.65   $70.65   $70.70  
  Purchase #3 $6.98   6.333%   $7.422   $7.42   $7.40   $7.40  
  Purchase #4 $245.80   4.620%   $257.156   $257.16   $257.15   $257.20  
  Purchase #5 $74.99   7.256%   $80.4313   $80.43   $80.45   $80.40  
  Purchase #6 $225.94   11.492%   $251.905   $251.91   $251.90   $251.90  
  Purchase #7 $221.46   11.590%   $247.1272   $247.13   $247.15   $247.10  
  7 purchase totals = $925.31       $1,012.3086   $1,012.32   $1,012.30   $1,012.30