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 $250.85   9.202%   $273.9332   $273.93   $273.95   $273.90  
  Purchase #2 $120.45   8.465%   $130.6461   $130.65   $130.65   $130.60  
  Purchase #3 $73.82   9.751%   $81.0182   $81.02   $81.00   $81.00  
  Purchase #4 $57.45   3.609%   $59.5234   $59.52   $59.50   $59.50  
  Purchase #5 $157.34   8.351%   $170.4795   $170.48   $170.50   $170.50  
  Purchase #6 $243.71   8.415%   $264.2182   $264.22   $264.20   $264.20  
  Purchase #7 $25.32   10.581%   $27.9991   $28.00   $28.00   $28.00  
  7 purchase totals = $928.94       $1,007.8177   $1,007.82   $1,007.80   $1,007.70