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 $189.81   13.297%   $215.049   $215.05   $215.05   $215.00  
  Purchase #2 $138.59   5.102%   $145.6609   $145.66   $145.65   $145.70  
  Purchase #3 $67.29   3.793%   $69.8423   $69.84   $69.85   $69.80  
  Purchase #4 $88.76   5.112%   $93.2974   $93.30   $93.30   $93.30  
  Purchase #5 $145.96   10.694%   $161.569   $161.57   $161.55   $161.60  
  Purchase #6 $33.65   10.811%   $37.2879   $37.29   $37.30   $37.30  
  Purchase #7 $184.26   5.183%   $193.8102   $193.81   $193.80   $193.80  
  7 purchase totals = $848.32       $916.5167   $916.52   $916.50   $916.50