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 $167.62   10.164%   $184.6569   $184.66   $184.65   $184.70  
  Purchase #2 $49.67   10.146%   $54.7095   $54.71   $54.70   $54.70  
  Purchase #3 $145.71   7.132%   $156.102   $156.10   $156.10   $156.10  
  Purchase #4 $247.95   13.274%   $280.8629   $280.86   $280.85   $280.90  
  Purchase #5 $19.59   13.382%   $22.2115   $22.21   $22.20   $22.20  
  Purchase #6 $98.47   3.249%   $101.6693   $101.67   $101.65   $101.70  
  Purchase #7 $152.49   12.344%   $171.3134   $171.31   $171.30   $171.30  
  7 purchase totals = $881.50       $971.5255   $971.52   $971.45   $971.60