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 $162.84   10.714%   $180.2867   $180.29   $180.30   $180.30  
  Purchase #2 $187.97   9.324%   $205.4963   $205.50   $205.50   $205.50  
  Purchase #3 $216.28   12.852%   $244.0763   $244.08   $244.10   $244.10  
  Purchase #4 $140.26   5.221%   $147.583   $147.58   $147.60   $147.60  
  Purchase #5 $239.25   12.324%   $268.7352   $268.74   $268.75   $268.70  
  Purchase #6 $62.99   8.166%   $68.1338   $68.13   $68.15   $68.10  
  Purchase #7 $216.80   4.415%   $226.3717   $226.37   $226.35   $226.40  
  7 purchase totals = $1,226.39       $1,340.6830   $1,340.69   $1,340.75   $1,340.70