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 $169.98   5.506%   $179.3391   $179.34   $179.35   $179.30  
  Purchase #2 $134.73   11.655%   $150.4328   $150.43   $150.45   $150.40  
  Purchase #3 $23.96   7.256%   $25.6985   $25.70   $25.70   $25.70  
  Purchase #4 $200.35   3.206%   $206.7732   $206.77   $206.75   $206.80  
  Purchase #5 $78.44   10.753%   $86.8747   $86.87   $86.85   $86.90  
  Purchase #6 $56.51   6.333%   $60.0888   $60.09   $60.10   $60.10  
  Purchase #7 $206.52   5.441%   $217.7568   $217.76   $217.75   $217.80  
  7 purchase totals = $870.49       $926.9639   $926.96   $926.95   $927.00