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 $30.37   11.118%   $33.7465   $33.75   $33.75   $33.70  
  Purchase #2 $150.85   6.131%   $160.0986   $160.10   $160.10   $160.10  
  Purchase #3 $171.40   5.469%   $180.7739   $180.77   $180.75   $180.80  
  Purchase #4 $212.44   5.109%   $223.2936   $223.29   $223.30   $223.30  
  Purchase #5 $67.62   9.618%   $74.1237   $74.12   $74.10   $74.10  
  Purchase #6 $164.99   7.845%   $177.9335   $177.93   $177.95   $177.90  
  Purchase #7 $69.52   9.162%   $75.8894   $75.89   $75.90   $75.90  
  7 purchase totals = $867.19       $925.8592   $925.85   $925.85   $925.80