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 $98.52   5.582%   $104.0194   $104.02   $104.00   $104.00  
  Purchase #2 $219.37   12.794%   $247.4362   $247.44   $247.45   $247.40  
  Purchase #3 $19.33   5.480%   $20.3893   $20.39   $20.40   $20.40  
  Purchase #4 $221.26   4.598%   $231.4335   $231.43   $231.45   $231.40  
  Purchase #5 $123.64   11.676%   $138.0762   $138.08   $138.10   $138.10  
  Purchase #6 $196.58   3.174%   $202.8194   $202.82   $202.80   $202.80  
  Purchase #7 $222.74   3.488%   $230.5092   $230.51   $230.50   $230.50  
  7 purchase totals = $1,101.44       $1,174.6832   $1,174.69   $1,174.70   $1,174.60