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 $230.49   4.562%   $241.005   $241.01   $241.00   $241.00  
  Purchase #2 $147.83   8.485%   $160.3734   $160.37   $160.35   $160.40  
  Purchase #3 $243.72   13.521%   $276.6734   $276.67   $276.65   $276.70  
  Purchase #4 $51.74   11.659%   $57.7724   $57.77   $57.75   $57.80  
  Purchase #5 $203.48   12.214%   $228.333   $228.33   $228.35   $228.30  
  Purchase #6 $104.66   8.753%   $113.8209   $113.82   $113.80   $113.80  
  Purchase #7 $168.95   10.655%   $186.9516   $186.95   $186.95   $187.00  
  7 purchase totals = $1,150.87       $1,264.9297   $1,264.92   $1,264.85   $1,265.00