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 $177.78   5.351%   $187.293   $187.29   $187.30   $187.30  
  Purchase #2 $54.26   12.635%   $61.1158   $61.12   $61.10   $61.10  
  Purchase #3 $100.85   7.803%   $108.7193   $108.72   $108.70   $108.70  
  Purchase #4 $73.43   13.163%   $83.0956   $83.10   $83.10   $83.10  
  Purchase #5 $54.87   12.200%   $61.5641   $61.56   $61.55   $61.60  
  Purchase #6 $243.98   9.498%   $267.1532   $267.15   $267.15   $267.20  
  Purchase #7 $234.49   3.425%   $242.5213   $242.52   $242.50   $242.50  
  7 purchase totals = $939.66       $1,011.4623   $1,011.46   $1,011.40   $1,011.50