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 $189.89   8.850%   $206.6953   $206.70   $206.70   $206.70  
  Purchase #2 $118.91   3.728%   $123.343   $123.34   $123.35   $123.30  
  Purchase #3 $150.31   3.257%   $155.2056   $155.21   $155.20   $155.20  
  Purchase #4 $198.82   4.405%   $207.578   $207.58   $207.60   $207.60  
  Purchase #5 $182.30   10.158%   $200.818   $200.82   $200.80   $200.80  
  Purchase #6 $98.29   9.862%   $107.9834   $107.98   $108.00   $108.00  
  Purchase #7 $160.86   10.644%   $177.9819   $177.98   $178.00   $178.00  
  7 purchase totals = $1,099.38       $1,179.6052   $1,179.61   $1,179.65   $1,179.60