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 $65.88   3.707%   $68.3222   $68.32   $68.30   $68.30  
  Purchase #2 $167.75   8.760%   $182.4449   $182.44   $182.45   $182.40  
  Purchase #3 $203.42   7.493%   $218.6623   $218.66   $218.65   $218.70  
  Purchase #4 $204.65   11.178%   $227.5258   $227.53   $227.55   $227.50  
  Purchase #5 $143.37   7.348%   $153.9048   $153.90   $153.90   $153.90  
  Purchase #6 $229.95   6.191%   $244.1862   $244.19   $244.20   $244.20  
  Purchase #7 $147.61   12.666%   $166.3063   $166.31   $166.30   $166.30  
  7 purchase totals = $1,162.63       $1,261.3525   $1,261.35   $1,261.35   $1,261.30