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 $173.87   13.260%   $196.9252   $196.93   $196.95   $196.90  
  Purchase #2 $91.96   11.304%   $102.3552   $102.36   $102.35   $102.40  
  Purchase #3 $226.79   4.587%   $237.1929   $237.19   $237.20   $237.20  
  Purchase #4 $202.96   8.495%   $220.2015   $220.20   $220.20   $220.20  
  Purchase #5 $216.44   11.427%   $241.1726   $241.17   $241.15   $241.20  
  Purchase #6 $71.96   3.496%   $74.4757   $74.48   $74.50   $74.50  
  Purchase #7 $9.31   3.111%   $9.5996   $9.60   $9.60   $9.60  
  7 purchase totals = $993.29       $1,081.9227   $1,081.93   $1,081.95   $1,082.00