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 $109.71   11.788%   $122.6426   $122.64   $122.65   $122.60  
  Purchase #2 $22.33   4.629%   $23.3637   $23.36   $23.35   $23.40  
  Purchase #3 $42.98   5.199%   $45.2145   $45.21   $45.20   $45.20  
  Purchase #4 $213.84   12.753%   $241.111   $241.11   $241.10   $241.10  
  Purchase #5 $150.51   11.834%   $168.3214   $168.32   $168.30   $168.30  
  Purchase #6 $212.52   10.202%   $234.2013   $234.20   $234.20   $234.20  
  Purchase #7 $161.31   3.293%   $166.6219   $166.62   $166.60   $166.60  
  7 purchase totals = $913.20       $1,001.4764   $1,001.46   $1,001.40   $1,001.40