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 $184.25   9.372%   $201.5179   $201.52   $201.50   $201.50  
  Purchase #2 $122.74   6.434%   $130.6371   $130.64   $130.65   $130.60  
  Purchase #3 $28.43   11.853%   $31.7998   $31.80   $31.80   $31.80  
  Purchase #4 $117.64   9.236%   $128.5052   $128.51   $128.50   $128.50  
  Purchase #5 $179.64   4.688%   $188.0615   $188.06   $188.05   $188.10  
  Purchase #6 $135.45   6.578%   $144.3599   $144.36   $144.35   $144.40  
  Purchase #7 $96.67   10.312%   $106.6386   $106.64   $106.65   $106.60  
  7 purchase totals = $864.82       $931.5200   $931.53   $931.50   $931.50