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 $20.96   9.846%   $23.0237   $23.02   $23.00   $23.00  
  Purchase #2 $206.46   4.872%   $216.5187   $216.52   $216.50   $216.50  
  Purchase #3 $52.32   8.816%   $56.9325   $56.93   $56.95   $56.90  
  Purchase #4 $169.38   11.282%   $188.4895   $188.49   $188.50   $188.50  
  Purchase #5 $243.43   9.283%   $266.0276   $266.03   $266.05   $266.00  
  Purchase #6 $245.62   8.274%   $265.9426   $265.94   $265.95   $265.90  
  Purchase #7 $74.50   3.696%   $77.2535   $77.25   $77.25   $77.30  
  7 purchase totals = $1,012.67       $1,094.1881   $1,094.18   $1,094.20   $1,094.10