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 $175.58   9.819%   $192.8202   $192.82   $192.80   $192.80  
  Purchase #2 $59.53   3.790%   $61.7862   $61.79   $61.80   $61.80  
  Purchase #3 $101.96   11.698%   $113.8873   $113.89   $113.90   $113.90  
  Purchase #4 $183.82   3.585%   $190.4099   $190.41   $190.40   $190.40  
  Purchase #5 $231.81   13.148%   $262.2884   $262.29   $262.30   $262.30  
  Purchase #6 $238.95   10.767%   $264.6777   $264.68   $264.70   $264.70  
  Purchase #7 $31.43   11.504%   $35.0457   $35.05   $35.05   $35.00  
  7 purchase totals = $1,023.08       $1,120.9154   $1,120.93   $1,120.95   $1,120.90