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 $139.41   5.156%   $146.598   $146.60   $146.60   $146.60  
  Purchase #2 $166.85   3.291%   $172.341   $172.34   $172.35   $172.30  
  Purchase #3 $156.82   6.574%   $167.1293   $167.13   $167.15   $167.10  
  Purchase #4 $210.55   7.384%   $226.097   $226.10   $226.10   $226.10  
  Purchase #5 $35.98   9.620%   $39.4413   $39.44   $39.45   $39.40  
  Purchase #6 $109.51   7.790%   $118.0408   $118.04   $118.05   $118.00  
  Purchase #7 $175.76   10.462%   $194.148   $194.15   $194.15   $194.10  
  7 purchase totals = $994.88       $1,063.7954   $1,063.80   $1,063.85   $1,063.60