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 $91.45   7.173%   $98.0097   $98.01   $98.00   $98.00  
  Purchase #2 $215.94   4.678%   $226.0417   $226.04   $226.05   $226.00  
  Purchase #3 $135.94   3.485%   $140.6775   $140.68   $140.70   $140.70  
  Purchase #4 $176.71   4.478%   $184.6231   $184.62   $184.60   $184.60  
  Purchase #5 $12.69   12.818%   $14.3166   $14.32   $14.30   $14.30  
  Purchase #6 $209.53   5.436%   $220.9201   $220.92   $220.90   $220.90  
  Purchase #7 $194.57   3.363%   $201.1134   $201.11   $201.10   $201.10  
  7 purchase totals = $1,036.83       $1,085.7021   $1,085.70   $1,085.65   $1,085.60