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 $219.85   10.465%   $242.8573   $242.86   $242.85   $242.90  
  Purchase #2 $165.55   4.834%   $173.5527   $173.55   $173.55   $173.60  
  Purchase #3 $111.31   4.811%   $116.6651   $116.67   $116.65   $116.70  
  Purchase #4 $181.52   5.497%   $191.4982   $191.50   $191.50   $191.50  
  Purchase #5 $219.29   9.497%   $240.116   $240.12   $240.10   $240.10  
  Purchase #6 $90.44   7.763%   $97.4609   $97.46   $97.45   $97.50  
  Purchase #7 $70.65   6.355%   $75.1398   $75.14   $75.15   $75.10  
  7 purchase totals = $1,058.61       $1,137.2900   $1,137.30   $1,137.25   $1,137.40