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 $213.91   12.807%   $241.3055   $241.31   $241.30   $241.30  
  Purchase #2 $157.27   13.139%   $177.9337   $177.93   $177.95   $177.90  
  Purchase #3 $80.52   3.498%   $83.3366   $83.34   $83.35   $83.30  
  Purchase #4 $120.67   3.301%   $124.6533   $124.65   $124.65   $124.70  
  Purchase #5 $82.87   13.447%   $94.0135   $94.01   $94.00   $94.00  
  Purchase #6 $89.27   11.570%   $99.5985   $99.60   $99.60   $99.60  
  Purchase #7 $236.43   9.219%   $258.2265   $258.23   $258.25   $258.20  
  7 purchase totals = $980.94       $1,079.0676   $1,079.07   $1,079.10   $1,079.00