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 $197.74   3.532%   $204.7242   $204.72   $204.70   $204.70  
  Purchase #2 $54.30   7.650%   $58.454   $58.45   $58.45   $58.50  
  Purchase #3 $212.91   3.692%   $220.7706   $220.77   $220.75   $220.80  
  Purchase #4 $184.42   4.283%   $192.3187   $192.32   $192.30   $192.30  
  Purchase #5 $149.85   6.799%   $160.0383   $160.04   $160.05   $160.00  
  Purchase #6 $192.45   7.544%   $206.9684   $206.97   $206.95   $207.00  
  Purchase #7 $7.97   7.446%   $8.5634   $8.56   $8.55   $8.60  
  7 purchase totals = $999.64       $1,051.8376   $1,051.83   $1,051.75   $1,051.90