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 $116.43   5.278%   $122.5752   $122.58   $122.60   $122.60  
  Purchase #2 $94.57   4.839%   $99.1462   $99.15   $99.15   $99.10  
  Purchase #3 $102.27   6.112%   $108.5207   $108.52   $108.50   $108.50  
  Purchase #4 $29.65   9.668%   $32.5166   $32.52   $32.50   $32.50  
  Purchase #5 $195.78   4.127%   $203.8598   $203.86   $203.85   $203.90  
  Purchase #6 $183.98   3.832%   $191.0301   $191.03   $191.05   $191.00  
  Purchase #7 $205.66   9.367%   $224.9242   $224.92   $224.90   $224.90  
  7 purchase totals = $928.34       $982.5728   $982.58   $982.55   $982.50