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 $243.68   8.753%   $265.0093   $265.01   $265.00   $265.00  
  Purchase #2 $101.35   11.717%   $113.2252   $113.23   $113.25   $113.20  
  Purchase #3 $223.95   7.672%   $241.1314   $241.13   $241.15   $241.10  
  Purchase #4 $177.37   5.860%   $187.7639   $187.76   $187.75   $187.80  
  Purchase #5 $196.65   3.379%   $203.2948   $203.29   $203.30   $203.30  
  Purchase #6 $21.93   6.519%   $23.3596   $23.36   $23.35   $23.40  
  Purchase #7 $233.56   3.244%   $241.1367   $241.14   $241.15   $241.10  
  7 purchase totals = $1,198.49       $1,274.9209   $1,274.92   $1,274.95   $1,274.90