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 $87.47   7.541%   $94.0661   $94.07   $94.05   $94.10  
  Purchase #2 $107.91   13.265%   $122.2243   $122.22   $122.20   $122.20  
  Purchase #3 $151.79   9.140%   $165.6636   $165.66   $165.65   $165.70  
  Purchase #4 $100.31   12.436%   $112.7846   $112.78   $112.80   $112.80  
  Purchase #5 $53.66   5.526%   $56.6253   $56.63   $56.65   $56.60  
  Purchase #6 $144.68   11.347%   $161.0968   $161.10   $161.10   $161.10  
  Purchase #7 $31.27   10.394%   $34.5202   $34.52   $34.50   $34.50  
  7 purchase totals = $677.09       $746.9809   $746.98   $746.95   $747.00