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 $174.76   5.262%   $183.9559   $183.96   $183.95   $184.00  
  Purchase #2 $139.77   7.541%   $150.3101   $150.31   $150.30   $150.30  
  Purchase #3 $157.25   3.530%   $162.8009   $162.80   $162.80   $162.80  
  Purchase #4 $145.66   5.600%   $153.817   $153.82   $153.80   $153.80  
  Purchase #5 $120.44   5.146%   $126.6378   $126.64   $126.65   $126.60  
  Purchase #6 $201.55   3.709%   $209.0255   $209.03   $209.05   $209.00  
  Purchase #7 $38.57   6.532%   $41.0894   $41.09   $41.10   $41.10  
  7 purchase totals = $978.00       $1,027.6366   $1,027.65   $1,027.65   $1,027.60