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 $60.38   8.569%   $65.554   $65.55   $65.55   $65.60  
  Purchase #2 $203.39   3.479%   $210.4659   $210.47   $210.45   $210.50  
  Purchase #3 $211.80   5.451%   $223.3452   $223.35   $223.35   $223.30  
  Purchase #4 $134.79   9.494%   $147.587   $147.59   $147.60   $147.60  
  Purchase #5 $174.34   8.730%   $189.5599   $189.56   $189.55   $189.60  
  Purchase #6 $101.53   8.807%   $110.4717   $110.47   $110.45   $110.50  
  Purchase #7 $22.73   8.458%   $24.6525   $24.65   $24.65   $24.70  
  7 purchase totals = $908.96       $971.6362   $971.64   $971.60   $971.80