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 $62.45   12.675%   $70.3655   $70.37   $70.35   $70.40  
  Purchase #2 $103.86   6.695%   $110.8134   $110.81   $110.80   $110.80  
  Purchase #3 $105.96   4.112%   $110.3171   $110.32   $110.30   $110.30  
  Purchase #4 $194.97   6.422%   $207.491   $207.49   $207.50   $207.50  
  Purchase #5 $211.44   3.421%   $218.6734   $218.67   $218.65   $218.70  
  Purchase #6 $173.53   11.605%   $193.6682   $193.67   $193.65   $193.70  
  Purchase #7 $95.45   13.339%   $108.1821   $108.18   $108.20   $108.20  
  7 purchase totals = $947.66       $1,019.5107   $1,019.51   $1,019.45   $1,019.60