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 $52.49   3.714%   $54.4395   $54.44   $54.45   $54.40  
  Purchase #2 $62.99   3.748%   $65.3509   $65.35   $65.35   $65.40  
  Purchase #3 $247.45   10.108%   $272.4622   $272.46   $272.45   $272.50  
  Purchase #4 $24.34   5.552%   $25.6914   $25.69   $25.70   $25.70  
  Purchase #5 $198.52   6.749%   $211.9181   $211.92   $211.90   $211.90  
  Purchase #6 $132.53   4.187%   $138.079   $138.08   $138.10   $138.10  
  Purchase #7 $165.84   11.467%   $184.8569   $184.86   $184.85   $184.90  
  7 purchase totals = $884.16       $952.7980   $952.80   $952.80   $952.90