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 $83.46   9.637%   $91.503   $91.50   $91.50   $91.50  
  Purchase #2 $54.64   7.598%   $58.7915   $58.79   $58.80   $58.80  
  Purchase #3 $68.81   3.120%   $70.9569   $70.96   $70.95   $71.00  
  Purchase #4 $95.70   4.344%   $99.8572   $99.86   $99.85   $99.90  
  Purchase #5 $93.81   9.282%   $102.5174   $102.52   $102.50   $102.50  
  Purchase #6 $206.44   3.127%   $212.8954   $212.90   $212.90   $212.90  
  Purchase #7 $98.77   7.787%   $106.4612   $106.46   $106.45   $106.50  
  7 purchase totals = $701.63       $742.9826   $742.99   $742.95   $743.10