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 $184.55   10.424%   $203.7875   $203.79   $203.80   $203.80  
  Purchase #2 $156.29   9.635%   $171.3485   $171.35   $171.35   $171.30  
  Purchase #3 $24.38   7.138%   $26.1202   $26.12   $26.10   $26.10  
  Purchase #4 $230.85   4.591%   $241.4483   $241.45   $241.45   $241.40  
  Purchase #5 $33.38   7.831%   $35.994   $35.99   $36.00   $36.00  
  Purchase #6 $11.66   6.689%   $12.4399   $12.44   $12.45   $12.40  
  Purchase #7 $170.52   4.284%   $177.8251   $177.83   $177.85   $177.80  
  7 purchase totals = $811.63       $868.9635   $868.97   $869.00   $868.80