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 $193.59   8.353%   $209.7606   $209.76   $209.75   $209.80  
  Purchase #2 $23.82   8.282%   $25.7928   $25.79   $25.80   $25.80  
  Purchase #3 $151.47   5.608%   $159.9644   $159.96   $159.95   $160.00  
  Purchase #4 $180.51   12.263%   $202.6459   $202.65   $202.65   $202.60  
  Purchase #5 $243.99   6.578%   $260.0397   $260.04   $260.05   $260.00  
  Purchase #6 $123.80   5.168%   $130.198   $130.20   $130.20   $130.20  
  Purchase #7 $38.39   8.345%   $41.5936   $41.59   $41.60   $41.60  
  7 purchase totals = $955.57       $1,029.9950   $1,029.99   $1,030.00   $1,030.00