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 $170.65   6.296%   $181.3941   $181.39   $181.40   $181.40  
  Purchase #2 $202.80   7.572%   $218.156   $218.16   $218.15   $218.20  
  Purchase #3 $105.46   11.609%   $117.7029   $117.70   $117.70   $117.70  
  Purchase #4 $71.50   13.475%   $81.1346   $81.13   $81.15   $81.10  
  Purchase #5 $204.68   3.557%   $211.9605   $211.96   $211.95   $212.00  
  Purchase #6 $186.57   7.263%   $200.1206   $200.12   $200.10   $200.10  
  Purchase #7 $216.79   11.129%   $240.9166   $240.92   $240.90   $240.90  
  7 purchase totals = $1,158.45       $1,251.3853   $1,251.38   $1,251.35   $1,251.40