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 $191.49   6.158%   $203.282   $203.28   $203.30   $203.30  
  Purchase #2 $209.63   11.319%   $233.358   $233.36   $233.35   $233.40  
  Purchase #3 $48.27   7.640%   $51.9578   $51.96   $51.95   $52.00  
  Purchase #4 $24.28   3.448%   $25.1172   $25.12   $25.10   $25.10  
  Purchase #5 $228.72   12.634%   $257.6165   $257.62   $257.60   $257.60  
  Purchase #6 $203.74   10.827%   $225.7989   $225.80   $225.80   $225.80  
  Purchase #7 $6.64   5.579%   $7.0104   $7.01   $7.00   $7.00  
  7 purchase totals = $912.77       $1,004.1408   $1,004.15   $1,004.10   $1,004.20