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 $191.74   4.692%   $200.7364   $200.74   $200.75   $200.70  
  Purchase #2 $31.32   7.162%   $33.5631   $33.56   $33.55   $33.60  
  Purchase #3 $220.60   5.464%   $232.6536   $232.65   $232.65   $232.70  
  Purchase #4 $11.96   13.841%   $13.6154   $13.62   $13.60   $13.60  
  Purchase #5 $150.44   6.524%   $160.2547   $160.25   $160.25   $160.30  
  Purchase #6 $237.96   3.698%   $246.7598   $246.76   $246.75   $246.80  
  Purchase #7 $70.43   4.702%   $73.7416   $73.74   $73.75   $73.70  
  7 purchase totals = $914.45       $961.3246   $961.32   $961.30   $961.40