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 $214.34   8.602%   $232.7775   $232.78   $232.80   $232.80  
  Purchase #2 $23.65   3.487%   $24.4747   $24.47   $24.45   $24.50  
  Purchase #3 $88.42   9.243%   $96.5927   $96.59   $96.60   $96.60  
  Purchase #4 $228.74   7.201%   $245.2116   $245.21   $245.20   $245.20  
  Purchase #5 $239.37   9.607%   $262.3663   $262.37   $262.35   $262.40  
  Purchase #6 $120.96   11.753%   $135.1764   $135.18   $135.20   $135.20  
  Purchase #7 $75.71   7.402%   $81.3141   $81.31   $81.30   $81.30  
  7 purchase totals = $991.19       $1,077.9133   $1,077.91   $1,077.90   $1,078.00