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 $157.60   9.172%   $172.0551   $172.06   $172.05   $172.10  
  Purchase #2 $102.56   12.109%   $114.979   $114.98   $115.00   $115.00  
  Purchase #3 $181.33   11.835%   $202.7904   $202.79   $202.80   $202.80  
  Purchase #4 $100.51   10.262%   $110.8243   $110.82   $110.80   $110.80  
  Purchase #5 $204.40   4.128%   $212.8376   $212.84   $212.85   $212.80  
  Purchase #6 $48.31   3.226%   $49.8685   $49.87   $49.85   $49.90  
  Purchase #7 $242.73   10.292%   $267.7118   $267.71   $267.70   $267.70  
  7 purchase totals = $1,037.44       $1,131.0667   $1,131.07   $1,131.05   $1,131.10