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 $249.93   13.424%   $283.4806   $283.48   $283.50   $283.50  
  Purchase #2 $8.43   3.807%   $8.7509   $8.75   $8.75   $8.80  
  Purchase #3 $235.61   13.782%   $268.0818   $268.08   $268.10   $268.10  
  Purchase #4 $169.34   5.456%   $178.5792   $178.58   $178.60   $178.60  
  Purchase #5 $23.99   11.459%   $26.739   $26.74   $26.75   $26.70  
  Purchase #6 $244.63   9.819%   $268.6502   $268.65   $268.65   $268.70  
  Purchase #7 $56.50   6.168%   $59.9849   $59.98   $60.00   $60.00  
  7 purchase totals = $988.43       $1,094.2666   $1,094.26   $1,094.35   $1,094.40