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 $247.94   7.702%   $267.0363   $267.04   $267.05   $267.00  
  Purchase #2 $42.87   11.368%   $47.7435   $47.74   $47.75   $47.70  
  Purchase #3 $25.52   9.173%   $27.8609   $27.86   $27.85   $27.90  
  Purchase #4 $229.98   6.181%   $244.1951   $244.20   $244.20   $244.20  
  Purchase #5 $203.52   13.701%   $231.4043   $231.40   $231.40   $231.40  
  Purchase #6 $189.69   8.130%   $205.1118   $205.11   $205.10   $205.10  
  Purchase #7 $96.77   5.691%   $102.2772   $102.28   $102.30   $102.30  
  7 purchase totals = $1,036.29       $1,125.6291   $1,125.63   $1,125.65   $1,125.60