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 $31.32   10.252%   $34.5309   $34.53   $34.55   $34.50  
  Purchase #2 $190.93   7.284%   $204.8373   $204.84   $204.85   $204.80  
  Purchase #3 $218.97   9.714%   $240.2407   $240.24   $240.25   $240.20  
  Purchase #4 $222.89   5.607%   $235.3874   $235.39   $235.40   $235.40  
  Purchase #5 $10.84   3.799%   $11.2518   $11.25   $11.25   $11.30  
  Purchase #6 $201.88   10.108%   $222.286   $222.29   $222.30   $222.30  
  Purchase #7 $95.26   7.669%   $102.5655   $102.57   $102.55   $102.60  
  7 purchase totals = $972.09       $1,051.0996   $1,051.11   $1,051.15   $1,051.10