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 $69.49   6.149%   $73.7629   $73.76   $73.75   $73.80  
  Purchase #2 $102.28   9.453%   $111.9485   $111.95   $111.95   $111.90  
  Purchase #3 $235.84   7.751%   $254.12   $254.12   $254.10   $254.10  
  Purchase #4 $168.52   7.741%   $181.5651   $181.57   $181.55   $181.60  
  Purchase #5 $229.82   6.833%   $245.5236   $245.52   $245.50   $245.50  
  Purchase #6 $83.45   6.300%   $88.7074   $88.71   $88.70   $88.70  
  Purchase #7 $140.54   12.324%   $157.8601   $157.86   $157.85   $157.90  
  7 purchase totals = $1,029.94       $1,113.4876   $1,113.49   $1,113.40   $1,113.50