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 $60.65   11.151%   $67.4131   $67.41   $67.40   $67.40  
  Purchase #2 $157.88   12.440%   $177.5203   $177.52   $177.50   $177.50  
  Purchase #3 $92.43   12.279%   $103.7795   $103.78   $103.80   $103.80  
  Purchase #4 $69.52   7.325%   $74.6123   $74.61   $74.60   $74.60  
  Purchase #5 $238.30   3.744%   $247.222   $247.22   $247.20   $247.20  
  Purchase #6 $36.57   12.288%   $41.0637   $41.06   $41.05   $41.10  
  Purchase #7 $214.58   7.298%   $230.24   $230.24   $230.25   $230.20  
  7 purchase totals = $869.93       $941.8509   $941.84   $941.80   $941.80