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 $83.35   11.538%   $92.9669   $92.97   $92.95   $93.00  
  Purchase #2 $183.84   10.399%   $202.9575   $202.96   $202.95   $203.00  
  Purchase #3 $208.47   8.542%   $226.2775   $226.28   $226.30   $226.30  
  Purchase #4 $31.45   9.841%   $34.545   $34.55   $34.55   $34.50  
  Purchase #5 $198.35   12.185%   $222.5189   $222.52   $222.50   $222.50  
  Purchase #6 $55.43   3.670%   $57.4643   $57.46   $57.45   $57.50  
  Purchase #7 $243.92   5.800%   $258.0674   $258.07   $258.05   $258.10  
  7 purchase totals = $1,004.81       $1,094.7975   $1,094.81   $1,094.75   $1,094.90