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 $83.93   13.492%   $95.2538   $95.25   $95.25   $95.30  
  Purchase #2 $185.92   4.805%   $194.8535   $194.85   $194.85   $194.90  
  Purchase #3 $53.28   12.220%   $59.7908   $59.79   $59.80   $59.80  
  Purchase #4 $119.41   8.264%   $129.278   $129.28   $129.30   $129.30  
  Purchase #5 $127.61   11.560%   $142.3617   $142.36   $142.35   $142.40  
  Purchase #6 $203.52   7.759%   $219.3111   $219.31   $219.30   $219.30  
  Purchase #7 $23.27   10.254%   $25.6561   $25.66   $25.65   $25.70  
  7 purchase totals = $796.94       $866.5050   $866.50   $866.50   $866.70