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 $186.33   6.212%   $197.9048   $197.90   $197.90   $197.90  
  Purchase #2 $227.70   6.284%   $242.0087   $242.01   $242.00   $242.00  
  Purchase #3 $59.27   7.260%   $63.573   $63.57   $63.55   $63.60  
  Purchase #4 $203.26   5.130%   $213.6872   $213.69   $213.70   $213.70  
  Purchase #5 $180.91   7.489%   $194.4583   $194.46   $194.45   $194.50  
  Purchase #6 $157.49   3.753%   $163.4006   $163.40   $163.40   $163.40  
  Purchase #7 $228.28   11.121%   $253.667   $253.67   $253.65   $253.70  
  7 purchase totals = $1,243.24       $1,328.6996   $1,328.70   $1,328.65   $1,328.80