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 $119.36   11.444%   $133.0196   $133.02   $133.00   $133.00  
  Purchase #2 $75.55   4.368%   $78.85   $78.85   $78.85   $78.90  
  Purchase #3 $144.64   8.214%   $156.5207   $156.52   $156.50   $156.50  
  Purchase #4 $209.27   4.514%   $218.7164   $218.72   $218.70   $218.70  
  Purchase #5 $202.30   5.108%   $212.6335   $212.63   $212.65   $212.60  
  Purchase #6 $33.87   8.461%   $36.7357   $36.74   $36.75   $36.70  
  Purchase #7 $173.45   5.351%   $182.7313   $182.73   $182.75   $182.70  
  7 purchase totals = $958.44       $1,019.2072   $1,019.21   $1,019.20   $1,019.10