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 $23.58   4.821%   $24.7168   $24.72   $24.70   $24.70  
  Purchase #2 $181.93   12.317%   $204.3383   $204.34   $204.35   $204.30  
  Purchase #3 $84.39   9.634%   $92.5201   $92.52   $92.50   $92.50  
  Purchase #4 $10.61   9.666%   $11.6356   $11.64   $11.65   $11.60  
  Purchase #5 $118.35   11.703%   $132.2005   $132.20   $132.20   $132.20  
  Purchase #6 $159.74   10.397%   $176.3482   $176.35   $176.35   $176.30  
  Purchase #7 $211.77   3.729%   $219.6669   $219.67   $219.65   $219.70  
  7 purchase totals = $790.37       $861.4264   $861.44   $861.40   $861.30