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 $52.30   11.244%   $58.1806   $58.18   $58.20   $58.20  
  Purchase #2 $138.71   13.316%   $157.1806   $157.18   $157.20   $157.20  
  Purchase #3 $147.33   10.428%   $162.6936   $162.69   $162.70   $162.70  
  Purchase #4 $193.42   13.785%   $220.0829   $220.08   $220.10   $220.10  
  Purchase #5 $239.81   12.510%   $269.8102   $269.81   $269.80   $269.80  
  Purchase #6 $189.76   4.258%   $197.84   $197.84   $197.85   $197.80  
  Purchase #7 $124.56   5.590%   $131.5229   $131.52   $131.50   $131.50  
  7 purchase totals = $1,085.89       $1,197.3108   $1,197.30   $1,197.35   $1,197.30