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 $45.86   13.334%   $51.975   $51.98   $52.00   $52.00  
  Purchase #2 $73.32   10.422%   $80.9614   $80.96   $80.95   $81.00  
  Purchase #3 $55.37   4.327%   $57.7659   $57.77   $57.75   $57.80  
  Purchase #4 $212.49   9.160%   $231.9541   $231.95   $231.95   $232.00  
  Purchase #5 $77.30   8.167%   $83.6131   $83.61   $83.60   $83.60  
  Purchase #6 $49.52   13.419%   $56.1651   $56.17   $56.15   $56.20  
  Purchase #7 $147.50   7.410%   $158.4298   $158.43   $158.45   $158.40  
  7 purchase totals = $661.36       $720.8644   $720.87   $720.85   $721.00