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 $84.44   3.456%   $87.3582   $87.36   $87.35   $87.40  
  Purchase #2 $208.98   9.146%   $228.0933   $228.09   $228.10   $228.10  
  Purchase #3 $221.56   4.159%   $230.7747   $230.77   $230.75   $230.80  
  Purchase #4 $194.67   12.709%   $219.4106   $219.41   $219.40   $219.40  
  Purchase #5 $58.50   12.197%   $65.6352   $65.64   $65.65   $65.60  
  Purchase #6 $81.69   11.341%   $90.9545   $90.95   $90.95   $91.00  
  Purchase #7 $67.77   9.156%   $73.975   $73.98   $74.00   $74.00  
  7 purchase totals = $917.61       $996.2015   $996.20   $996.20   $996.30